In HVAC systems, zoning is becoming increasingly popular in residential buildings as it allows a finer regulation of the temperature and flow of energy. The flow of fluid, e.g. air, i.e. its amount or volume, into a zone, e.g. an enclosed space or room in a building, is controlled by an actuated valve or damper. The position of the valve or damper is controlled depending on the measurement of the thermostat in each zone and demand, e.g. a desired temperature in the zone. The demand is set by a user or by a computerized system that anticipates the user's demand. A new generation of thermostats is capable of learning users' habits to anticipate the needs in different zones. Moreover, the new generation of thermostats can be connected to a telecommunications network and can incorporate and consider in their anticipatory algorithms outside information, such as climatic region, altitude, and/or weather predictions.
Flow of air in a zone may be affected by the closing and opening of other dampers in the HVAC system, making the system often quite instable. To obtain pressure-independence of the air flow in the zone, flow sensors are implemented in the air duct and the damper position is controlled in response to the demand and the actual flow value.
In variable air volume (VAV) HVAC systems with multiple zones, the closing of all dampers leads to possible mechanical damage of the duct work and often to an inacceptable noise level. Furthermore, if all dampers but one are closed, the regulation of the flow becomes increasingly difficult, as the position of the damper has to be controlled within a small range because of the excess system pressure.
To overcome some of these problems, in a first solution of the prior art, a fan with variable speed is used. The speed of the ventilator is adjusted by a local controller depending on the position of the damper with the largest opening. The applicant is selling such a solution under the name “Fan Optimiser”.
In a second solution of the prior art, a modulating bypass damper is used to maintain the overall system pressure (after the bypass damper) within reasonable limits. However, often it is not possible to retrofit existing HVAC system installations with the addition of such a bypass damper.